Induction sealing plastic parts together by heating metal embedded in one of the plastic parts, or by heating metal components clamping the parts together, is old in the art. Heat is developed by generating a high frequency oscillating magnetic field in the presence of the metal. Depending on the metal, either eddy current losses or magnetic hysteresis losses are believed responsible for heating the metal. Heat from the metal is then conducted through the plastic parts to their sealable interface. Plastic melting occurs from the conducted heat. If the plastic materials are compatible and sufficient pressure is applied, the plastic parts can be fusion welded together. Once the magnetic induction field is removed, the heat may be dissipated from the sealable interface through the metal contacting the plastic parts. Cooling the sealable interface under pressure is generally required to produce a strong seal. The great benefit of the induction heating process is that heat can be quickly generated in low mass metal dies so that high production rates can be achieved.
Squeezebottle dispensers having fluid-containing, flexible inner bags sealed within them are also common in the art. When such a dispenser is squeezed, fluid is forced from the bag through a discharge opening at the top of the dispenser. Valving in the dispenser enables air to be compressed within the squeezebottle during squeezing, but valving then allows air to vent into the bottle to replace the dispensed fluid after the squeezebottle is released. Repeated squeezing cycles cause the bag to collapse around the fluid within the squeezebottle as the bag empties.
A problem with such dispensers is that a bag tends to collapse most quickly near its discharge opening. This is believed due to higher velocity fluid flow at the discharge opening causing lower static pressure there. Fluid flow may be choked off from the rest of the bag if the bag collapses prematurely at the discharge opening. To correct this problem, the manner in which the inner bag can collapse is generally controlled. For example, bags may be designed to collapse radially about a perforated diptube connected to the discharge opening. When the fluid is highly viscous like toothpaste, however, diptubes provide too much resistance to fluid flow through them. For fluids having viscosities great enough that the fluid cannot flow under gravity, another collapse control approach is often used. That is, a bag is sealed to the midline circumference of the squeezebottle so that the bag can collapse by inverting axially toward the discharge opening. Bag inversion offers minimum flow resistance.
For squeezebottle dispensers having inner bags which invert toward the discharge opening, there is a construction problem of inserting and sealing a bag inside a squeezebottle. The discharge opening of the squeezebottle is usually smaller in circumference than the inner side wall of the squeezebottle, so that the discharge opening may later be capped with a reasonably sized closure. If the bag is inserted into the squeezebottle from a small diameter discharge opening, it is difficult to insert a sealing tool into the bag to seal the bag to the midline circumference of the squeezebottle. The sealing tool must expand to press the bag against the inner side wall of the squeezebottle. A reliable, high speed method for midline bag sealing, using such an expanding tool, is not currently known.
Alternatively, if the bag is inserted from the opposite end of the squeezebottle, which is usually the bottom of the squeezebottle, the bag must later be filled and sealed closed from the bottom end, and a bottom piece must be added to close the open bottom of the squeezebottle. For example, twisting the open end of the bag after filling and then heat sealing the twisted portion is one approach to closing a filled bag. Closing the bag after filling has been found to be a slow and difficult process.
One solution to the bottom end bag insertion and filling problem for highly viscous fluids is a construction that seals a half bag to the midline circumference of a squeezebottle. A half bag may be inserted from the open bottom of the squeezebottle with its closed end at the discharge opening of the squeezebottle. After sealing the open end of the half bag to the midline circumference of the squeezebottle, the half bag may then be inverted so that its closed end is positioned at the bottom of the squeezebottle. Filling may then be accomplished from the discharge opening of the dispenser. Such a construction requires a complete seal around the midline circumference of the squeezebottle.
The half bag approach enables conventional high speed filling without subsequent bag closing and sealing. However, the half bag approach also requires the formation and handling of a half bag and the inversion of the half bag after sealing it to the squeezebottle. Bag forming and internal sealing operations are complex and difficult even when performed manually.